The invention relates to a method for improving the total production of useful energy of an internal combustion engine producing heat and mechanical energy, herein sometimes referred to as a "thermal power engine," and to an engine intended for the application of this method.
In operation of a thermal power engine, the energy content of fuel supplied to the engine is converted partly to mechanical energy, which is made available at a mechanical power output of the engine, and partly to thermal energy, of which a portion is removed from the engine by the engine's cooling system. In order to maximize the overall efficiency of the engine, it is desirable that the thermal energy be applied to a useful purpose and not discharged as waste heat.
In known large internal combustion engines, such as for example large diesel engines, the cooling system of the engine often raises the temperature of the coolant to a level that is less than 100.degree. C., usually in the range 80.degree. C. to 85.degree. C. It is difficult to find a useful application for waste heat at such low temperature values, and consequently a significant part of the energy content of the fuel consumed will not be used for useful purposes. In some rather large plants employing thermal power engines the thermal energy of the coolant has however been used, by means of heat exchangers, to produce, for example, warm water (e.g. warm process water) or for district heating applications.
A thermal power plant may comprise several thermal power engines, whereby the total power output of the plant may be of the order of magnitude of 100 MW. The greater is the power of a thermal power engine or a power plant containing such engines, the more important for energy saving it is to find a useful application for its waste heat and the better are the chances that the investments made for waste heat recovery will prove to be profitable.